Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02P—IGNITION, OTHER THAN COMPRESSION IGNITION, FOR INTERNAL-COMBUSTION ENGINES; TESTING OF IGNITION TIMING IN COMPRESSION-IGNITION ENGINES
  • F02P5/00—Advancing or retarding ignition; Control therefor
  • F02P5/04—Advancing or retarding ignition; Control therefor automatically, as a function of the working conditions of the engine or vehicle or of the atmospheric conditions
  • F02P5/145—Advancing or retarding ignition; Control therefor automatically, as a function of the working conditions of the engine or vehicle or of the atmospheric conditions using electrical means
  • F02P5/15—Digital data processing
  • F02P5/152—Digital data processing dependent on pinking
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
  • G01L23/00—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid
  • G01L23/22—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid for detecting or indicating knocks in internal-combustion engines; Units comprising pressure-sensitive members combined with ignitors for firing internal-combustion engines
  • G01L23/221—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid for detecting or indicating knocks in internal-combustion engines; Units comprising pressure-sensitive members combined with ignitors for firing internal-combustion engines for detecting or indicating knocks in internal combustion engines
  • G01L23/225—Devices or apparatus for measuring or indicating or recording rapid changes, such as oscillations, in the pressure of steam, gas, or liquid; Indicators for determining work or energy of steam, internal-combustion, or other fluid-pressure engines from the condition of the working fluid for detecting or indicating knocks in internal-combustion engines; Units comprising pressure-sensitive members combined with ignitors for firing internal-combustion engines for detecting or indicating knocks in internal combustion engines circuit arrangements therefor
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/40—Engine management systems

Definitions

• This invention relates generally to the measuring of knock in an internal combustion engine and more particularly to a method of measuring knock in an internal combustion engine.
• Knock is caused by improper ignition of fuel in an internal combustion engine. Improper ignition results in decreased engine performance and increased emissions. Knock, furthermore, generates acoustic vibrations which propagate throughout the engine structure, and possibly other adjoining structures. These vibrations, coupled with a rapid rate of pressure rise in the combustion chamber, may promote accelerated wearing of engine components. Wear may be even faster for engines operating with natural gas, due to a higher rate of pressure rise in the combustion chamber as compared with gasoline powered engines.
• Detonation in an engine may be sensed by either a pressure sensor or a vibration sensor.
• Pressure sensing will provide only a knock signal; however, it is very costly where pressures are high, as in a diesel engine.
• Vibration sensing to measure the magnitude of detonation in an engine is difficult.
• Noise and vibrations unrelated to knock contaminate vibration sensor signals.
• Contaminated signals require complex filtering in order to detect signal components related to detonation.
• expensive sensors that may provide cleaner signals requiring less complex filtering.
• sensor outputs fluctuate, thus inhibiting precise measurement of knock. For example, even supposedly identical accelerometers often vary due to manufacturing techniques, and as operating conditions change, the accelerometers deliver inaccurate signals.
• Prior systems provide means for detecting knock and controlling selected engine operating parameters to reduce the knock to an acceptable level. Recently these efforts have been directed to sensing knock induced vibrations by monitoring one or more characteristic frequencies corresponding to the acoustic cavity resonance modes of the combustion chamber. These characteristic frequencies generally act as carrier waves and are amplitude modulated by the knock level vibrations. When demodulated, the magnitude of the envelope of the carrier wave denotes the magnitude of the knock. Discovering and monitoring cavity resonance frequencies reduces the amount of filtering needed to obtain acceptable detonation information. This information is typically used to reduce knock by retarding the spark advance. For example, U.S. Patent #4,364,260 issued to Chen et al.
• the present invention is directed to overcoming one or more of the problems as set forth above.
• a method for measuring the magnitude of knock in an internal combustion engine having at least one combustion chamber.
• a signal responsive to vibrations of an engine is transmitted and then is filtered in a frequency band about a cavity resonance frequency of a combustion chamber of the engine.
• the filtered signal is demodulated to produce an envelope of the filtered signal.
• the maximum and minimum of the envelope is detected, and a ratio of each maximum to each respective minimum is determined. The ratio is correlative to the magnitude of knock in the engine.
• an apparatus measures the magnitude of knock in an internal combustion engine having a plurality of combustion chambers.
• An accelerometer is mounted on a bank of the combustion chambers and arranged to deliver an electrical signal responsive to vibrations of the engine.
• a filter is tuned to pass frequencies of the received electrical signal in a band about a cavity resonance frequency of the combustion chambers.
• a demodulator detects the envelope of the filtered electrical signal. Means is provided for detecting the maximum and minimum magnitudes of each envelope. A means determines the ratio of each maximum to each respective minimum, the ratio being correlative to the magnitude of knock in the engine.
• Determination of engine knock is important in the field of electronic engine controls.
• An engine operates at peak efficiency with a small amount of detonation. Therefore accurately detecting and measuring the magnitude of engine knock directly affects the efficiency of an engine control.
• acoustic cavity resonance frequencies of combustion chambers in an engine carry knock signals. If these frequencies are isolated, through filtering, knock can be detected.
• accurate measurement of engine knock does not necessarily follow accurate detection. Since vibration sensors vary, even among supposedly “identical” sensors, accurate measurement remains a problem.
• each sensor is divided by the minimum relative output.
• the effects of sensor drifting are negated.
• the resulting ratio is correlative to the magnitude of the detonation, and can be used in an-engine timing control.
• Fig. 1 is a block diagram of a preferred embodiment of the detonation measuring apparatus
• Fig. 2 diagrammaticly illustrates a knock signal
• Fig. 3, on sheet 1 of the drawings, is a circuit diagram of a portion of the preferred embodiment of the detonation measuring apparatus
• Fig. 4 is a circuit diagram of another portion of the preferred embodiment.
• Fig. 5 is a flowchart depicting a portion of software of the preferred embodiment.
• Fig. 6 is a flowchart depicting another portion of software of the preferred embodiment.
• an apparatus 10 for measuring the magnitude of knock in an internal combustion engine such as a diesel engine 14.
• Knock is commonly understood to as an explosive detonation or autoignition of end gas in a combustion chamber which produces a metallic sound.
• a method for measureing the magnitude of knock includes transmitting a signal responsive to vibrations of the engine 14. The transmitted signal is filtered in a frequency band about a cavity resonance frequency of a combustion chamber of the engine 14. The filtered signal is demodulated to produce an envelope of the filtered signal. Maximums and minimums of each envelope are detected. A ratio of each maximum to each respective minimum is determined. The ratio is correlative to the magnitude of engine knock.
• This method is set forth generally with respect to Figs. 1 and 2, and more particularly with respect to Figs. 3, 4, 5, and 6.
• Fig. 1 shows a vibration sensor, such as an accelerometer 12, mounted on engine 14.
• the engine 14 is an internal combustion engine having at least one combustion chamber 16,18,20,22,24, and 26.
• the accelerometer 12 is of a kind commercially available and is tuned to sense vibrations in a range about a cavity resonance frequency of at least one combustion chamber.
• f is frequency in hertz; c is the speed of sound; £ is a non-dimensional number; and
• D is the combustion chamber diameter
• the cavity resonant frequency f varies directly with the speed of sound and inversely with the diameter D.
• the speed of sound changes with the temperature of the combustion chamber, which rises as engine load increases. Therefore, the cavity resonant frequency f changes during engine operation.
• the first mode cavity resonance frequency is sensed to obtain an indication of engine knock. Therefore, the accelerometer 12 senses vibrations corresponding to a cavity resonance frequency f, including resonance frequency fluctuations during engine operation.
• Fig. 2 shows a typical knock induced signal.
• a carrier wave 28 is amplitude modulated by the level of detonation.
• the carrier wave 28 is demodulated to create an envelope 30 which, as illustrated in Fig. 2, has a maximum value at A and a minumum value at B occuring during a preselected time indicated as t.
• the length of time t preferably includes several firings of the cylinders in one bank of the engine. While time t has been shown as including only one detonation, there could be several detonations in a severe case.
• the envelope 30 varies in amplitude and contains information concerning engine knock.
• the accelerometer 12 transmits this type of signal to a channel 31, which includes an amplifier 32, a bandpass filter 34, a demodulator 36, and a peak and valley detector 38, all shown in Fig. 1.
• the amplifier 32, the bandpass filter 34, the demodualtor 36, and the peak and valley detector 38 are all of known design and function to those skilled in the art. Accordingly the detailed circuitry of these components is not discussed at length herein.
• the amplifier 32 receives the vibration signal from the accelerometer 12.
• the amplifier 32 amplifies and buffers the vibration signal, and delivers an amplified signal to a bandpass filter 34.
• the bandpass filter 34 filters the amplified signal, and passes only signals having frequencies within a range about the chosen mode of the cavity resonance frequency f.
• engine experiments determine the range of fluctuation of a cavity resonance frequency during the operation cycle of the engine. For instance, the first cavity resonance frequency for a large engine may be 4K Hz using equation 1.
• the bandpass filter 34 should pass a frequency band from 2.5K Hz to 5.5K Hz to insure knock detection throughout the engine's operating cycle.
• the filtered signal is passed to a demodulator 36, which detects the envelope 30 of the carrier wave 28.
• the envelope 30 varies in amplitude in response to knock, hence the waveform of the envelope 30 is a good indicator of the magnitude of engine knock.
• the envelope 30 is a knock signal which passes to a peak and valley detector 38.
• the peak and valley detector 38 detects the maximum magnitude A and the minimum magnitude B of the envelope.
• the accelerometer 12 produces a voltage signal having a magnitude responsive to the magnitude of the detonation.
• the maximum and minimum values will vary. Comparing the maximum of each time sample to the minimum of each time sample produces a more accurate indication of the magnitude of the detonation. This comparison effectively compares the peak detonation signal with background noise, thus eliminating the effect of the variation of the output of the sensor.
• a means 42 determines the ratio of the maximum magnitude of the envelope to the minimum magnitude of the envelope. This determination may be made in several ways, such as with a divider circuit or software, as described with respect to Fig. 5.
• the ratio of each maximum A to each respective minimum B is correlative to the magnitude of knock. The ratio minimizes sensor errors due to drift or calibration.
• the ratio may then be used as part of a timing control 44 to adjust the timing of the engine, via a magneto 46 for instance, in response to the magnitude of knock, as described with respect to Fig. 6.
• Figs. 3 and 4 show a circuit diagram of a preferred embodiment of the detonation measuring apparatus.
• the subsequently described embodiment represents a particular design choice.
• the circuitry forms a channel 31.
• a vibration sensor is preferably connected to each cylinder bank of a multicylinder engine in order to accurately detect knock in all cylinders.
• an in-line six cylinder engine uses one vibration sensor, while a V-8 uses two vibration sensors. Therefore, each vibration sensor uses a similar channel 31.
• Figs 3 and 4 illustrate the apparatus having one channel, but several channels may be used if needed.
• An accelerometer 12 is connected across a parallel resistor 50 to the input of an amplifier 32, shown here to be connected as a buffering amplifier 52.
• the output of the amplifier 32 is connected to the input of the first stage 54 of a bandpass filter 34.
• the first stage 54 includes a serially connected capacitor 56 and resistor 58 at the negative input of an operational amplifier 60.
• a capacitor 62 in parallel with a resistor 64 are disposed in the negative feedback loop of the operational amplifier 60, and a resistor 66 is connected at the output of the operational amplifier 60.
• the positive input of the operational amplifier 60 is connected to a reference voltage, vref.
• the second stage 68 of the bandpass filter 34 is shown in Fig. 4 as a three-pole filter.
• the filter includes three operational amplifiers 70,72,74 connected in series.
• each operational amplifier 70,72,74 The positive input of each operational amplifier 70,72,74 is connected to the reference voltage, vref.
• a resistor 76,78,80 in series with a respective capacitor 82,84,86 are connected to the negative input of each respective operational amplifier 70,72,74.
• each operational amplifier 70,72,74 has a resistor 88,90,92 connected across the negative feedback loop, and a capacitor 94,96,98 connected across the negative feedback loop and across the capacitor 82,84,86.
• the output of the bandpass filter 34 is connected to the input of a demodulator 36.
• the demodulator 36 receives the filtered signal and detects the envelope 30 of the carrier wave 28.
• the demodulator 36 includes an operational amplifier 100 having a diode 102 connected across the negative feedback loop.
• the output of the operational amplifier 100 is the anode of the diode 102.
• An RC filter 104 having a resistor 106 and a capacitor 108 receives the output of the operational amplifier 100.
• the diode 102 clips the incoming filtered signal so that only the portion above zero volts passes to the RC filter 104.
• the upper envelope is a mirror image of the lower envelope, thus the required detonation information may be obtained by processing either the upper or lower envelope.
• the RC filter 104 filters out the frequency of the carrier wave 28 leaving the frequency of the envelope 30 which is the detonation signal.
• the output of the demodulator 36 is connected to the input of the peak and valley detector 38.
• the peak and valley detector 38 detects the maximum magnitude and the minimum magnitude of the envelope.
• the peak detector 110 is quite similar in structure to the demodulator 36 described above.
• the peak detector 110 includes an operational amplifier 112 having a diode 114 connected across the negative feedback loop.
• the output of the operational amplifier 112 is the anode of the diode 114.
• An RC filter 116 having a resistor 118 and a capacitor 120 receives the output of the operational amplifier 112.
• the RC filter is selected to have a q-uick discharge time and a slow charge time in order to detect the peak quickly and hold it.
• the valley detector 122 is also quite similar in structure to the peak detector 110 and the demodulator 36.
• the diode 124 of the valley detector 122 is biased oppositely as compared to the peak detector 110, so the output of the operational amplifier 126 of the valley detector 122 is the cathode of the diode 124.
• the diode is biased oppositely to detect the negative portion of the envelope.
• the RC filter 128 at the output of the operational amplifier 126 is selected to have a quick charge time and a slow decay time in order to detect the valley quickly and hold it. Notice that in the demodulator 36 and in the peak detector 110, the resistors 106,118 and the capacitors 108,120 of the RC filters 104,116 are connected on one terminal to the output of the respective operational amplifiers 100,112 and are connected on the other terminal to the reference voltage, vref.
• the resistor 130 is connected on one terminal to the output of the operational amplifier 126 and on the other terminal to circuit ground to provide a decay path for the valley detector, while the capacitor 132 is connected on one terminal to the output of the operational amplifier 126 and on the other terminal to the reference voltage, vref.
• outputs of the peak and valley detector 38 are passed through an analog-to-digital converter (A/D) for application to a microprocessor, not shown.
• A/D analog-to-digital converter
• the microprocessor contains software, depicted in Figs. 5 and 6, which determines the ratio of the peak signal to the valley signal, relates the ratio to the magnitude of knock, and controls the timing of the engine in response to the magnitude of knock.
• Fig. 5 is a flowchart 150 depicting a portion of software of a preferred embodiment of the detonation measuring apparatus. As stated above, the software controls an associated microprocessor. The microprocessor reads the data from the peak and valley detector 38. In fact the microprocessor is capable of reading from several different channels 31, and the flowchart 150 depicts a situation employing two channels 31,31'.
• the software begins in a decision block 152, where the engine's acceleration is determined.
• the detonation ratio is set to zero in a block 154 and the loop ends. This is done to prevent false detection of knock due to engine vibrations in the knock frequency band which may occur during acceleration. Otherwise, control passes to a decision block 156 where the engine speed is determined. At low engine speeds, the detonation ratio is again set to zero in the block 154 and the loop ends. Since no detonation occurs at low speeds, the ratio is not monitored to prevent false detonation signals from external sources. Otherwise, control passes to a block 158 and the microprocessor reads the data from the peak detectors 110,110'. Control passes to a block 160 and the microprocessor saves the peak values from each peak detector 110,110' under the variable names MAX1 and MAX2, respectively.
• Control then passes to a block 162 and the microprocessor reads the data from the valley detectors 122,122'.
• Control passes to a block 164 and the microprocessor filters the valley signals with a low-pass filter having a time constant of 2.56 sec, for instance, which provides better sensitivity to detonation.
• the microprocessor then saves the valley values from each valley detector 122,122' under the variable names BKGND1 and BKGND2, respectively.
• Control passes to a block 166 where the ratio of MAX1 to BKGND1 is determined, and then to a block 168 where the ratio of MAX2 to BKGND2 is determined. These two ratios are compared one with another in a block 170 to determine a peak detonation ratio.
• the peak detonation ratio is the maximum of the two ratios, and is used in the timing control 44 to adjust the timing of the engine.
• Fig. 6 is a flowchart 174 depicting another portion of software of a preferred embodiment of the detonation measuring apparatus.
• the software controls the associated microprocessor to effect the timing control 44 function for the engine 14.
• the inputs to this portion of the software are consecutive peak detonation ratios derived in the previously described software.
• the peak detonation ratios are compared to various preselected setpoints to determine the magnitude of detonation.
• the peak detonation ratio is compared to a first preselected setpoint X which, for the illustrated engine is "16". If the peak detonation ratio is less than the first preselected setpoint X, control passes to a block 178 where a signal is delivered to advance the timing of the engine 14.
• Knock is a noise which occurs due to improper ignition of fuel in a combustion chamber. Poor timing, low fuel octane, and unsatisfactory fuel mixture all cause improper ignition. At times knock may be severe enough to cause engine damage.
• the apparatus 10 functions to accurately measure knock, and to control the timing of the engine in response to the magnitude of knock to maintain optimum combustion efficiency.
• An accelerometer 12 delivers vibration signals to an amplifier 32.
• the vibration signals generally have detonation signals modulated by a carrier frequency which corresponds to the cavity resonance frequency of the cylinder.
• the amplified signals pass to a bandpass filter 34 which passes portions of the amplified signal having frequency components within a range about the acoustic cavity resonance frequency.
• a demodulator 36 detects the envelope of the filtered signal, since the envelope contains the detonation signal.
• a peak and valley detector 38 detects the maximum and minimum of each detonation signal.
• the detected maximum and minimum of each detonation signal passes through an A/D converter to a microprocessor.
• the microprocessor determines the ratio of each maximum to each respective minimum, and produces a peak detonation signal.
• the peak detonation signal is then compared to a series of preselected setpoints to determine the magnitude of detonation. If the magnitude of detonation indicates a state of optimum combustion, the timing control 44 portion of the software does not effect a change in engine timing.
• the engine timing is advanced or retarded by a predetermined number of degrees in an attempt to achieve optimum combustion.
• the software reexecutes every loop, the magnitude of detonation is sampled and the timing controlled in response thereto.
• the microprocessor delivers an engine shutdown signal.
• a relay for controlling fuel delivery to the engine 14 is responsive to the engine shutdown signal. Upon reception of the engine shutdown signal, fuel delivery to the engine halts and the engine stops, thus preventing possible damage to the engine due to knock.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Signal Processing (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Combined Controls Of Internal Combustion Engines (AREA)
• Electrical Control Of Ignition Timing (AREA)

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• 1988
  • 1988-09-16 US US07/245,186 patent/US4895121A/en not_active Expired - Lifetime
  • 1988-11-16 WO PCT/US1988/004088 patent/WO1990002932A1/en active IP Right Grant
  • 1988-11-16 DE DE89904719T patent/DE3883015T2/de not_active Expired - Fee Related
  • 1988-11-16 JP JP1504644A patent/JP2577101B2/ja not_active Expired - Lifetime
  • 1988-11-16 BR BR888807799A patent/BR8807799A/pt not_active IP Right Cessation
  • 1988-11-16 EP EP89904719A patent/EP0423130B1/de not_active Expired - Lifetime
• 1989
  • 1989-08-28 CA CA000609578A patent/CA1330593C/en not_active Expired - Fee Related

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